Excimer laser apparatus and excimer laser system

ABSTRACT

An excimer laser apparatus includes a gas supply unit, connected to a first receptacle that holds a first laser gas containing halogen gas and a second receptacle that holds a second laser gas having a lower halogen gas concentration than the first laser gas, that supplies the first laser gas and the second laser gas to the interior of the laser chamber. Gas pressure control in which the gas supply unit supplies the second laser gas to the interior of the laser chamber or a gas exhaust unit partially exhausts gas from within the laser chamber, and partial gas replacement control in which the gas supply unit supplies the first laser gas and the second laser gas to the interior of the laser chamber and the gas exhaust unit partially exhausts gas from within the laser chamber sequentially, may be selectively performed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese Patent ApplicationNo. 2011-234057 filed Oct. 25, 2011, and Japanese Patent Application No.2012-160399 filed Jul. 19, 2012.

1. TECHNICAL FIELD

The present disclosure relates to excimer laser apparatuses and excimerlaser systems.

2. RELATED ART

The recent miniaturization and increased levels of integration ofsemiconductor integrated circuits has led to a demand for increases inthe resolutions of semiconductor exposure devices (called “exposuredevices” hereinafter). Accordingly, advances are being made in thereduction of the wavelengths of light emitted from exposure lightsources. Typically, gas laser apparatuses are being used as exposurelight sources instead of conventional mercury lamps. For example, a KrFexcimer laser apparatus that outputs ultraviolet laser light at awavelength of 248 nm and an ArF excimer laser apparatus that outputsultraviolet laser light at a wavelength of 193 nm are used as gas laserapparatuses for exposure.

SUMMARY

An excimer laser apparatus according to a first aspect of the presentdisclosure may include: a laser chamber containing a gas; at least apair of electrodes disposed within the laser chamber; a power sourceunit that supplies a voltage between the electrodes; a gas supply unit,connected to a first receptacle that holds a first laser gas containinghalogen gas and a second receptacle that holds a second laser gas havinga lower halogen gas concentration than the first laser gas, thatsupplies the first laser gas and the second laser gas to the interior ofthe laser chamber; a gas exhaust unit that partially exhausts gas fromwithin the laser chamber; and a gas control unit that controls the gassupply unit and the gas exhaust unit. The gas control unit mayselectively perform gas pressure control in which the gas supply unitsupplies the second laser gas to the interior of the laser chamber orthe gas exhaust unit partially exhausts gas from within the laserchamber, and partial gas replacement control in which the gas supplyunit supplies the first laser gas and the second laser gas to theinterior of the laser chamber and the gas exhaust unit partiallyexhausts gas from within the laser chamber sequentially.

An excimer laser system according to a second aspect of the presentdisclosure may include: a first excimer laser apparatus that includes afirst laser chamber containing a gas, at least a pair of firstelectrodes disposed within the first laser chamber, and a firstresonator disposed sandwiching the first laser chamber; a second excimerlaser apparatus that includes a second laser chamber containing a gas,at least a pair of second electrodes disposed within the second laserchamber, and a second resonator disposed sandwiching the second laserchamber, and that amplifies laser light outputted from the first excimerlaser apparatus; at least one power source unit that supplies a voltagebetween the first electrodes and the second electrodes; a gas supplyunit, connected to a first receptacle that holds a first laser gascontaining halogen gas and a second receptacle that holds a second lasergas having a lower halogen gas concentration than the first laser gas,that supplies the first laser gas and the second laser gas to theinteriors of the first laser chamber and the second laser chamber; a gasexhaust unit that partially exhausts gas from within the first laserchamber and the second laser chamber; and a gas control unit thatcontrols the gas supply unit and the gas exhaust unit. The gas controlunit may selectively perform: a first gas pressure control in which thegas supply unit supplies the second laser gas to the interior of thefirst laser chamber or the gas exhaust unit partially exhausts gas fromwithin the first laser chamber; a second gas pressure control in whichthe gas supply unit supplies the second laser gas to the interior of thesecond laser chamber or the gas exhaust unit partially exhausts gas fromwithin the second laser chamber; a first partial gas replacement controlin which the gas supply unit supplies the first laser gas and the secondlaser gas to the interior of the first laser chamber and the gas exhaustunit partially exhausts gas from within the first laser chambersequentially; and a second partial gas replacement control in which thegas supply unit supplies the first laser gas and the second laser gas tothe interior of the second laser chamber and the gas exhaust unitpartially exhausts gas from within the second laser chambersequentially.

An excimer laser apparatus according to a third aspect of the presentdisclosure may include: a laser chamber containing a gas; at least apair of electrodes disposed within the laser chamber; a power sourceunit that supplies a voltage between the electrodes; a gas supply unit,connected to a first receptacle that holds a first laser gas containinghalogen gas and a second receptacle that holds a second laser gas havinga lower halogen gas concentration than the first laser gas, thatsupplies the first laser gas and the second laser gas to the interior ofthe laser chamber; a gas exhaust unit that partially exhausts gas fromwithin the laser chamber; and a gas control unit that controls the gassupply unit and the gas exhaust unit. The gas control unit mayselectively perform partial gas replacement control in which the gassupply unit supplies the first laser gas and the second laser gas to theinterior of the laser chamber and the gas exhaust unit partiallyexhausts gas from within the laser chamber sequentially, and halogen gasfilling control in which the gas supply unit supplies the first lasergas to the interior of the laser chamber and the gas exhaust unitpartially exhausts gas from within the laser chamber sequentially.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present disclosure will be describedhereinafter with reference to the appended drawings.

FIG. 1 schematically illustrates the configuration of an excimer laserapparatus according to a first embodiment.

FIG. 2 is a state transition diagram illustrating gas control accordingto the first embodiment.

FIG. 3 is a flowchart illustrating gas control according to the firstembodiment.

FIG. 4 is a flowchart illustrating control of a voltage applied betweenelectrodes according to the first embodiment.

FIG. 5 is a flowchart illustrating the calculation of an excimer laserapparatus duty according to the first embodiment.

FIG. 6A is a flowchart illustrating a first example of a process thatcalculates a gas control interval, indicated in FIG. 3.

FIG. 6B is a graph illustrating a relationship between a duty of anexcimer laser apparatus and the gas control interval calculated as shownin FIG. 6A.

FIG. 6C is a flowchart illustrating a second example of a process thatcalculates a gas control interval, indicated in FIG. 3.

FIG. 6D is a graph illustrating a relationship between a duty of anexcimer laser apparatus and the gas control interval calculated as shownin FIG. 6C.

FIG. 6E is a flowchart illustrating a third example of a process thatcalculates a gas control interval, indicated in FIG. 3.

FIG. 6F is a graph illustrating a relationship between a duty of anexcimer laser apparatus and the gas control interval calculated as shownin FIG. 6E.

FIG. 7A is a flowchart illustrating a first example of a process thatcalculates a halogen gas partial pressure, indicated in FIG. 3.

FIG. 7B is a flowchart illustrating a second example of a process thatcalculates a halogen gas partial pressure, indicated in FIG. 3.

FIG. 7C is a flowchart illustrating a third example of a process thatcalculates a halogen gas partial pressure, indicated in FIG. 3.

FIG. 8A is a flowchart illustrating a first example of a process thatcalculates a gas replacement amount, indicated in FIG. 3.

FIG. 8B is a graph illustrating a relationship between a gas pressure ina laser chamber and the gas replacement amount calculated as shown inFIG. 8A.

FIG. 8C is a flowchart illustrating a second example of a process thatcalculates a gas replacement amount, indicated in FIG. 3.

FIG. 8D is a graph illustrating a relationship between a duty of anexcimer laser apparatus and the gas replacement amount calculated asshown in FIG. 8C.

FIG. 9 is a flowchart illustrating gas pressure control indicated inFIG. 3.

FIG. 10 is a flowchart illustrating a process for calculating areduction amount for a halogen gas partial pressure indicated in FIG. 9.

FIG. 11A is a graph illustrating changes in a gas pressure within alaser chamber and a voltage applied between electrodes resulting fromthe opening/closing of a second laser gas injection valve, indicated inFIG. 9.

FIG. 11B is a graph illustrating changes in a gas pressure within alaser chamber and a voltage applied between electrodes resulting fromthe opening/closing of an exhaust valve, indicated in FIG. 9.

FIG. 12 is a flowchart illustrating halogen gas filling controlindicated in FIG. 3.

FIG. 13 is a flowchart illustrating a process for calculating a firstlaser gas injection amount indicated in FIG. 12.

FIG. 14 is a graph illustrating changes in a gas pressure within a laserchamber resulting from the halogen gas filling control indicated in FIG.12.

FIG. 15 is a flowchart illustrating partial gas replacement controlindicated in FIG. 3.

FIG. 16 is a flowchart illustrating a process for calculating a firstlaser gas injection amount and a second laser gas injection amountindicated in FIG. 15.

FIG. 17 is a graph illustrating changes in a gas pressure within a laserchamber resulting from the partial gas replacement control indicated inFIG. 15.

FIG. 18 is a state transition diagram illustrating gas control accordingto a second embodiment.

FIG. 19 is a flowchart illustrating gas control according to the secondembodiment.

FIG. 20A is a flowchart illustrating a first example of a process thatcalculates a gas control interval, indicated in FIG. 19.

FIG. 20B is a graph illustrating a relationship between a duty of anexcimer laser apparatus and the gas control interval calculated as shownin FIG. 20A.

FIG. 20C is a flowchart illustrating a second example of a process thatcalculates a gas control interval, indicated in FIG. 19.

FIG. 20D is a graph illustrating a relationship between a duty of anexcimer laser apparatus and the gas control interval calculated as shownin FIG. 20C.

FIG. 21 is a flowchart illustrating partial gas replacement and halogengas filling control indicated in FIG. 19.

FIG. 22 is a flowchart illustrating a process for calculating a firstlaser gas injection amount and a second laser gas injection amountindicated in FIG. 21.

FIG. 23 schematically illustrates the configuration of an excimer lasersystem according to a third embodiment.

FIG. 24 is a state transition diagram illustrating gas control accordingto the third embodiment.

FIG. 25 is a flowchart illustrating gas control according to the thirdembodiment.

FIG. 26 is a state transition diagram illustrating gas control accordingto a fourth embodiment.

FIG. 27 is a flowchart illustrating gas control according to the fourthembodiment.

FIG. 28 schematically illustrates the configuration of an excimer lasersystem according to a fifth embodiment.

FIG. 29 is a flowchart illustrating gas control according to the fifthembodiment.

FIG. 30A schematically illustrates the configuration of an excimer lasersystem according to a sixth embodiment.

FIG. 30B schematically illustrates the configuration of a poweroscillator indicated in FIG. 30A.

DETAILED DESCRIPTION

Details

1. Outline 2. Explanation of Terms 3. Overall Description of ExcimerLaser Apparatus

3.1 Laser Chamber

3.2 Optical Resonator

3.3 Various Types of Sensors

3.4 Laser Control Unit

3.5 Gas Control Device

4. Gas Control in Excimer Laser Apparatus

4.1 Outline of Gas Control

4.2 Main Flow

4.3 Voltage Control by Laser Control Unit

4.4 Duty Calculation by Laser Control Unit

4.5 Calculation of Gas Control Interval (Details of S300)

4.6 Calculation of Halogen Gas Partial Pressure (Details of S400)

4.7 Calculation of Gas Replacement Amount (Details of S500)

4.8 Gas Pressure Control (Details of S600)

4.9 Halogen Gas Filling Control (Details of S700)

4.10 Partial Gas Replacement Control (Details of S800)

5. Second Embodiment (Integrated Control Including Partial GasReplacement Control and Halogen Gas Filling Control)

5.1 Outline of Gas Control

5.2 Main Flow

5.3 Calculation of Gas Control Interval (Details of S340)

5.4 Partial Gas Replacement and Halogen Gas Filling Control (Details ofS840)

6. Third Embodiment (MOPO System)

6.1 Overall Description of MOPO System

6.2 Gas Control in MOPO System

7. Fourth Embodiment (Integration of Control in MOPO System) 8. FifthEmbodiment (Integration of Chargers in MOPO System) 9. Sixth Embodiment(MOPO System Including Ring Resonator)

Embodiments of the present disclosure will be described in detailhereinafter with reference to the drawings. The embodiments describedhereinafter indicate several examples of the present disclosure, and arenot intended to limit the content of the present disclosure.Furthermore, not all of the configurations and operations described inthe embodiments are required configurations and operations in thepresent disclosure. Note that identical constituent elements will begiven identical reference numerals, and redundant descriptions thereofwill be omitted.

1. Outline

The output of desired pulsed laser light that is stable over a longperiod of time can be desired in an excimer laser apparatus for anexposure device. When laser oscillation is performed over a long periodof time in an excimer laser apparatus, impurities are produced within alaser chamber; when those impurities absorb laser light, worsen adischarge state, or the like, it is possible that the excimer laserapparatus will be unable to output the desired pulsed laser light. Insuch a case, it can be necessary to stop the laser oscillation, exhaustalmost all of the gas from within the laser chamber, and newly inject agas that will serve as a laser medium. This process is called “completegas replacement”. However, it is possible that the exposure device isunable to perform exposure while the laser oscillation is stopped.

According to one aspect of the present disclosure, gas pressure control,halogen gas filling control, and partial gas replacement control may becarried out selectively in a laser chamber during laser oscillation.Through this, a worsening of the environment within the laser chambercan be suppressed, and the number of complete gas replacements can besuppressed.

2. Explanation of Terms

Several terms used in the present application will be describedhereinafter.

A “first laser gas” may be a laser gas that contains a halogen gas.

A “second laser gas” may be a laser gas that has a lower concentrationof halogen gas than the first laser gas.

“Gas pressure control” may be control that either supplies the secondlaser gas to the interior of a laser chamber or partially exhausts gasfrom within the laser chamber.

“Halogen gas filling control” may be control that sequentially suppliesthe first laser gas to the interior of a laser chamber and thenpartially exhausts gas from within the laser chamber.

“Partial gas replacement control” may be control that sequentiallysupplies the first laser gas and the second laser gas to the interior ofa laser chamber and then partially exhausts gas from within the laserchamber.

3. Overall Description of Excimer Laser Apparatus

FIG. 1 schematically illustrates the configuration of an excimer laserapparatus according to a first embodiment. The excimer laser apparatusshown in FIG. 1 may include: a laser chamber 10; a pair of electrodes 11a and 11 b; a charger 12; a pulse power module (PPM) 13; a line narrowmodule 14; an output coupling mirror 15; a pressure sensor 16; anoptical sensor module 17; a laser control unit 30; and a gas controldevice 40. The excimer laser apparatus shown in FIG. 1 may be connectedto an exposure device 100 that carries out exposure using laser lightoutputted from the excimer laser apparatus.

3.1 Laser Chamber

The laser chamber 10 may be a chamber containing a laser gas serving asa laser medium, that contains, for example, argon, neon, fluorine, andthe like. The pair of electrodes 11 a and 11 b can be disposed withinthe laser chamber 10 as electrodes for pumping the laser medium througha discharge. The charger 12 may be configured of, for example, acapacitor connected to a power source device, and can hold electricalenergy for applying a high voltage between the pair of electrodes 11 aand 11 b. The pulse power module 13 may include a switch 13 a that iscontrolled by the laser control unit 30. When the switch 13 a changesfrom OFF to ON, the pulse power module 13 may generate a pulse-form highvoltage with the electrical energy held in the charger 12, and may applythat high voltage between the pair of electrodes 11 a and 11 b.

When the high voltage is applied between the pair of electrodes 11 a and11 b, a discharge can occur between the pair of electrodes 11 a and 11b. The laser medium within the laser chamber 10 can be pumped by theenergy of the discharge and can transition to a high-energy level. Whenthe pumped laser medium then transitions to a low-energy level, lightcan be emitted based on the difference between the energy levels.

Windows 10 a and 10 b may be provided at both ends of the laser chamber10. The light produced within the laser chamber 10 can be emitted to theexterior of the laser chamber 10 via the windows 10 a and 10 b.

3.2 Optical Resonator

The line narrow module 14 may include a prism 14 a and a grating 14 b.The prism 14 a can expand the beam width of the light emitted from thelaser chamber 10, and can allow that light to pass through to thegrating 14 b. In addition, the prism 14 a can reduce the beam width oflight reflected from the grating 14 b, and can allow that light to passthrough to the laser chamber 10. In addition, the prism 14 a can, whenallowing light to pass therethrough, refract the light to a differentangle in accordance with the wavelength of the light. Accordingly, theprism 14 a can function as a wavelength dispersion element.

The grating 14 b is configured of a highly-reflective material, and canbe a wavelength dispersion element in which many grooves are formed inthe surface thereof at predetermined intervals. Each groove may, forexample, be a triangular groove. The light that enters into the grating14 b from the prism 14 a can reflect in multiple directions that arevertical relative to the directions of the respective grooves (thevertical direction, in FIG. 1) at the sloped surfaces of thoserespective grooves. When the reflected light reflected at a given grooveoverlaps with the reflected light reflected at another given groove, thedifference in the optical path lengths between those instances ofreflected light depends on the angle of reflection of those instances ofreflected light. When the light is of a wavelength that corresponds tothe difference in the optical path lengths, the phases of the instancesof reflected light can match and reinforce each other, whereas when thelight is of a wavelength that does not correspond to the optical pathlength, the phases of the instances of reflected light do not match andcan weaken each other. Due to this interference effect, light in thevicinity of a specific wavelength based on the angle of reflection canbe extracted, and light that contains a large amount of that light ofthe specific wavelength can be returned to the laser chamber 10 via theprism 14 a.

In this manner, the line narrow module 14, which reduces the spectralwidth of laser light, can be configured by the prism 14 a and thegrating 14 b extracting light of a specific wavelength and returningthat light to the laser chamber 10.

The surface of the output coupling mirror 15 may be coated with apartially-reflective film. Accordingly, the output coupling mirror 15may allow some of the light outputted from the laser chamber 10 to passthrough, thus outputting that light, and may reflect the remainder ofthe light and return the reflected light to the interior of the laserchamber 10.

The distance between the output coupling mirror 15 and the grating 14 bcan be set to a distance at which light of a predetermined wavelengthoutputted from the laser chamber 10 forms a standing wave. Accordingly,an optical resonator can be configured from the line narrow module 14and the output coupling mirror 15. The light emitted from the laserchamber 10 can travel back and forth between the line narrow module 14and the output coupling mirror 15, and can be amplified each time itpasses between the electrode 11 a and the electrode 11 b (a laser gainspace) within the laser chamber 10. Some of the amplified light can thenbe outputted as output laser light via the output coupling mirror 15.

3.3 Various Types of Sensors

The pressure sensor 16 may detect a gas pressure within the laserchamber 10 and output that gas pressure to the gas control device 40.The optical sensor module 17 may include a beam splitter 17 a, afocusing optical system 17 b, and an optical sensor 17 c. The beamsplitter 17 a may allow the output laser light that has passed throughthe output coupling mirror 15 to pass through toward the exposure device100 at a high level of transmissibility, and may reflect some of theoutput laser light toward the focusing optical system 17 b. The focusingoptical system 17 b may focus the light reflected by the beam splitter17 a on to a photosensitive surface of the optical sensor 17 c. Theoptical sensor 17 c may detect a value regarding a pulse energy of thelaser light focused on the photosensitive surface, and may output, tothe laser control unit 30, data based on the detected value regardingthe pulse energy.

3.4 Laser Control Unit

The laser control unit 30 may exchange various types of signals with anexposure device controller 110 provided in the exposure device 100. Forexample, a laser light output start signal may be received from theexposure device controller 110. In addition, the laser control unit 30may send a charging voltage setting signal to the charger 12, aninstruction signal for turning a switch on or off to the pulse powermodule 13, or the like.

The laser control unit 30 may receive data based on the pulse energyfrom the optical sensor module 17, and may control the charging voltageof the charger 12 by referring to that data based on the pulse energy.The voltage applied between the pair of electrodes 11 a and 11 b may becontrolled by controlling the charging voltage of the charger 12.

In addition, the laser control unit 30 may count the number ofoscillation pulses in the excimer laser apparatus based on data receivedfrom the optical sensor module 17. In addition, the laser control unit30 may exchange various types of signals with a gas control unit 47provided in the gas control device 40. For example, the laser controlunit 30 may send, to the gas control device 40, data of the number ofoscillation pulses in the excimer laser apparatus.

3.5 Gas Control Device

The gas control device 40 may be connected to a first receptacle F2 thatcontains the first laser gas, which contains a halogen gas such asfluorine gas (F₂), and to a second receptacle B that contains the secondlaser gas, which contains a buffer gas. A mixed gas that is a mixture ofargon, neon, and fluorine may be used as the first laser gas. A mixedgas that is a mixture of argon and neon may be used as the second lasergas. Although valves may be provided at the gas extraction nozzles ofthe first receptacle F2 and the second receptacle B, it is preferablefor these valves to be open at least while the excimer laser apparatusis operational.

The gas control device 40 may include an exhaust pump 46, the gascontrol unit 47, and various types of valves and a mass flow controller,which will be described below. One end of a first pipe 41 may beconnected to the laser chamber 10, and a control valve C-V may beprovided in the first pipe 41. The other end of the first pipe 41 may beconnected to a second pipe 42 that is connected to the first receptacleF2, a third pipe 43 that is connected to the second receptacle B, and afourth pipe 44 that is connected to the exhaust pump 46.

A first laser gas injection valve F2-V that controls the supply of thefirst laser gas may be provided in the second pipe 42. The second pipe42 may branch in two ways, with a mass flow controller F2-MFC providedin one branch and a bypass valve F2-V2 provided in the other branch. Thebypass valve F2-V2 may be opened only when laser oscillation is stoppedand complete gas replacement is being carried out, and always closedduring laser oscillation. When the first laser gas is supplied to theinterior of the laser chamber 10 during laser oscillation, the controlvalve C-V and the first laser gas injection valve F2-V may be opened,and the flow rate of the first laser gas supplied to the interior of thelaser chamber 10 may be controlled by the mass flow controller F2-MFC.

A second laser gas injection valve B-V that controls the supply of thesecond laser gas may be provided in the third pipe 43. The third pipe 43may branch in two ways, with a mass flow controller B-MFC provided inone branch and a bypass valve B-V2 provided in the other branch. Thebypass valve B-V2 may be opened only when laser oscillation is stoppedand complete gas replacement is being carried out, and always closedduring laser oscillation. When the second laser gas is supplied to theinterior of the laser chamber 10 during laser oscillation, the controlvalve C-V and the second laser gas injection valve B-V may be opened,and the flow rate of the second laser gas supplied to the interior ofthe laser chamber 10 may be controlled by the mass flow controllerB-MFC.

An exhaust valve EX-V that controls the exhaust of gas from within thelaser chamber 10 may be provided in the fourth pipe 44. When controllingthe exhaust of gas from within the laser chamber 10, the exhaust pump 46may be driven and the exhaust valve EX-V and the control valve C-V maybe opened.

The gas control unit 47 may exchange various types of signals with thelaser control unit 30, and may furthermore receive data of a gaspressure within the laser chamber 10 from the pressure sensor 16. Thegas control unit 47 may control the control valve C-V, the first lasergas injection valve F2-V, the mass flow controller F2-MFC, the secondlaser gas injection valve B-V, the mass flow controller B-MFC, thebypass valve F2-V2, the bypass valve B-V2, the exhaust valve EX-V, theexhaust pump 46, and so on.

4. Gas Control in Excimer Laser Apparatus

4.1 Outline of Gas Control

FIG. 2 is a state transition diagram illustrating gas control accordingto the first embodiment. As shown in FIG. 2, the gas control accordingto the first embodiment may include gas pressure control (S600), halogengas filling control (S700), and partial gas replacement control (S800).A gas control stopped state (S0) may be included as well. These gascontrols may be carried out by the gas control unit 47 (FIG. 1).

The gas pressure control (S600) may be gas control for controlling theoutput of laser light by controlling the gas pressure within the laserchamber 10. In an excimer laser apparatus, the charging voltage of thecharger 12 can be controlled (that is, the voltage applied between thepair of electrodes 11 a and 11 b may be controlled) based on dataobtained from the optical sensor module 17, in order to hold the laserlight pulse energy at a desired value. For example, the voltage appliedbetween the pair of electrodes 11 a and 11 b can be increased in thecase where the laser light pulse energy tends to drop due to theinfluence of impurities within the laser chamber 10 or other operationalconditions. However, increasing or reducing the voltage too much cancause unstable discharges, which in turn can lead to the excimer laserapparatus operating in an unstable manner.

Accordingly, in the gas pressure control, a desired laser light outputmay be obtained by controlling the gas pressure within the laser chamber10, thus making it possible to avoid increasing or reducing the voltagetoo much. Specifically, in the case where a voltage V applied betweenthe pair of electrodes 11 a and 11 b is higher than a first thresholdVH, the gas pressure may be increased by supplying the second laser gasto the laser chamber 10. Likewise, in the case where the voltage Vapplied between the pair of electrodes 11 a and 11 b is lower than asecond threshold VL that is itself lower than the first threshold VH,the gas pressure may be reduced by partially exhausting the gas fromwithin the laser chamber 10.

The halogen gas filling control (S700) may be gas control for restoringthe halogen gas partial pressure that has dropped within the laserchamber 10 to a predetermined value. The inert gas of which the lasergas within the laser chamber 10 is configured is chemically stable, butthe halogen gas, such as fluorine, that configures the laser gas ishighly reactive with other matter, and easily results in impurities uponreacting with, for example, electrode materials. Accordingly, if laserlight is outputted for a long period of time, the halogen gas within thelaser chamber 10 can progressively decrease (that is, the halogen gaspartial pressure can decrease).

Accordingly, in the halogen gas filling control, the first laser gas maybe injected into the laser chamber 10 each time a predetermined amountof time passes, and the same amount (volume) as that injection amountmay be exhausted from the laser chamber 10.

The partial gas replacement control (S800) may be gas control forexhausting impurities from the laser chamber 10. In an excimer laserapparatus, the concentration of impurities within the laser chamber 10may rise progressively when laser light is outputted over a long periodof time, and it is possible that the desired pulsed laser light cannotbe outputted.

Accordingly, in the partial gas replacement control, the first laser gasand the second laser gas may be injected into the laser chamber 10 eachtime a predetermined amount of time passes, and the same amount (volume)as the total injection amount may be exhausted from the laser chamber10. In addition, the injection amount of the first laser gas and theinjection amount of the second laser gas may be calculated so that thehalogen gas partial pressure in the laser chamber 10 does not changebetween before and after the partial gas replacement control.

In the case where the conditions for gas pressure control (S600) are inplace, the gas control unit 47 (FIG. 1) may transit from the gas controlstopped state (S0) to the gas pressure control, and in the case wherethe gas pressure control has ended, may transit from the gas pressurecontrol to the gas control stopped state.

In the case where the conditions for the halogen gas filling control(S700) are in place, the gas control unit 47 may transit from the gascontrol stopped state (S0) to the halogen gas filling control, and inthe case where the halogen gas filling control has ended, may transitfrom the halogen gas filling control to the gas control stopped state.

In the case where the conditions for the partial gas replacement control(S800) are in place, the gas control unit 47 may transit from the gascontrol stopped state (S0) to the partial gas replacement control, andin the case where the partial gas replacement control has ended, maytransit from the partial gas replacement control to the gas controlstopped state.

4.2 Main Flow

FIG. 3 is a flowchart illustrating the gas control according to thefirst embodiment. The processes shown in FIG. 3 may be carried out bythe gas control unit 47 (FIG. 1). The processes shown in FIG. 3 caninclude the gas pressure control (S600), the halogen gas filling control(S700), and the partial gas replacement control (S800).

First, the gas control unit 47 may load default values required for thegas control (S100). These default values may include, for example,various types of proportionality constants, thresholds used for control,and so on. The proportionality constants may, for example, be a, b, c,g, h, k, and so on as mentioned later, and the thresholds may be thefirst threshold VH, the second threshold VL, and so on, also mentionedlater. Time measurement performed by timers Th and Tp may be started aswell.

Next, the gas control unit 47 may load the voltage V, a duty D, and agas pressure P (S200). The voltage V may be a voltage supplied betweenthe pair of electrodes 11 a and 11 b, and may be received from the lasercontrol unit 30. The duty D may be a ratio of a maximum value of arepetition rate of laser light relative to the overall cycle (that is, aduty), and may be received from the laser control unit 30. The gaspressure P may be the gas pressure within the laser chamber 10, and maybe received from the pressure sensor 16.

Next, the gas control unit 47 may calculate a time interval Thi for thehalogen gas filling control and a time interval Tpi for the partial gasreplacement control (S300). Details of these calculation processes willbe provided later.

Next, the gas control unit 47 may calculate a halogen gas partialpressure Ph within the laser chamber 10 (S400). Details of thiscalculation process will be provided later.

Next, the gas control unit 47 may calculate a gas replacement amount Qused in the partial gas replacement control (S500). Details of thiscalculation process will be provided later.

Next, the gas control unit 47 may compare the voltage V supplied betweenthe pair of electrodes 11 a and 11 b with the first threshold VH and thesecond threshold VL (S590). In the case where the voltage V is notwithin the range from the first threshold VH to the second threshold VL(V<VL or VH<V), it may be determined that the conditions for gaspressure control are in place, and the gas control unit 47 may thencarry out the gas pressure control (S600). Details of the gas pressurecontrol will be given later. When the gas pressure control has ended,the process may return to the aforementioned S200, and various types ofparameters may be loaded. As will be discussed later, there are cases,in the gas pressure control, where the halogen gas partial pressure Phdrops during control for reducing the gas pressure; therefore, byreturning to the aforementioned S200, the halogen gas partial pressurePh can be recalculated and the halogen gas filling control and the likecan be carried out properly.

In the case where the voltage V is within the range from the firstthreshold VH to the second threshold VL (VL VH), the gas control unit 47may compare the timer Th with the time interval Thi of the halogen gasfilling control (S690) In the case where the timer Th has reached thetime interval Thi of the halogen gas filling control (Thi<Th), it may bedetermined that the conditions for halogen gas filling control are inplace, and the gas control unit 47 may carry out the halogen gas fillingcontrol (S700). Details of the halogen gas filling control will be givenlater. When the halogen gas filling control has ended, the timer Th maybe reset (S780).

In the case where the timer Th has not reached the time interval Thi ofthe halogen gas filling control (Thi Th), or after the timer Th has beenreset (S780), the gas control unit 47 may compare the timer Tp with thetime interval Tpi of the partial gas replacement control (S790). In thecase where the timer Tp has reached the time interval Tpi of the partialgas replacement control (Tpi<Tp), it may be determined that theconditions for the partial gas replacement control are in place, and thegas control unit 47 may carry out the partial gas replacement control(S800). Details of the partial gas replacement control will be givenlater. When the partial gas replacement control has ended, the timer Tpmay be reset (S880).

In the case where the timer Tp has not reached the time interval Tpi ofthe partial gas replacement control (Tpi Tp), or after the timer Tp hasbeen reset (S880), the gas control unit 47 may determine whether or notto stop the gas control (S900). The determination as to whether or notto stop the gas control may be carried out based on whether or not astop signal has been received from the laser control unit 30. In thecase where the gas control is to be stopped (S900: YES), the processillustrated in this flowchart may end. However, in the case where thegas control is not to be stopped (S900: NO), the process may return tothe aforementioned S200, and various types of parameters may be loaded.

4.3 Voltage Control by Laser Control Unit

FIG. 4 is a flowchart illustrating control of a voltage applied betweenelectrodes according to the first embodiment. The processes shown inFIG. 4 may be carried out by the laser control unit 30 (FIG. 1)independent from the gas control shown in FIG. 3. In the processingshown in FIG. 4, the charging voltage of the charger 12 may becontrolled (that is, the voltage applied between the pair of electrodes11 a and 11 b may be controlled), based on data obtained from theoptical sensor module 17, in order to hold the laser light pulse energyat a desired value. Although the processes shown in FIG. 4 are carriedout separately from the gas control shown in FIG. 3, the followingdescriptions assume that the gas control can be a prerequisite.

First, the laser control unit 30 may load the value of a target pulseenergy Et for the laser light (S10). The value of the target pulseenergy Et may, for example, be a value required by the configuration ofthe exposure device 100.

Next, the laser control unit 30 may determine whether or not laseroscillation has been started (S11). Whether or not the laser oscillationhas been started may be determined based on whether or not the lasercontrol unit 30 has sent various types of signals for laser oscillationto the charger 12 and the pulse power module 13. Alternatively, whetheror not the laser oscillation has been started may be determined based onwhether or not data of a pulse energy E has been received from theoptical sensor module 17.

Next, the laser control unit 30 may load the value of the pulse energy Efor the laser light (S12). The value of the pulse energy E may be avalue received from the optical sensor module 17.

Next, the laser control unit 30 may compare the value of the pulseenergy E for the laser light with the value of the target pulse energyEt of the laser light (S13).

In the case where the value of the pulse energy E is equal to the valueof the target pulse energy Et (E=Et), the laser control unit 30 may holdthe voltage V applied between the pair of electrodes 11 a and 11 b at apresent value V (S14: V=V).

However, in the case where the value of the pulse energy E is less thanthe value of the target pulse energy Et (E<Et), the laser control unit30 may increase the voltage V applied between the pair of electrodes 11a and 11 b to a value in which a predetermined fluctuation amount ΔV hasbeen added to the present value V (S15: V=V+ΔV). Through this, the pulseenergy E can be raised and brought closer to the target pulse energy Et.

Meanwhile, in the case where the value of the pulse energy E is greaterthan the value of the target pulse energy Et (E>Et), the laser controlunit 30 may reduce the voltage V applied between the pair of electrodes11 a and 11 b to a value in which the predetermined fluctuation amountΔV has been subtracted from the present value (S16: V=V−ΔV). Throughthis, the pulse energy E can be reduced and brought closer to the targetpulse energy Et.

When the control of the voltage V (one of S14 through S16) has ended,the laser control unit 30 may send data of the voltage V to the gascontrol unit 47 (S17). Through this, the gas control unit 47 candetermine (S590) whether or not the conditions for the gas pressurecontrol (S600) shown in FIG. 3 are in place.

Next, the laser control unit 30 may determine whether or not the voltageV is greater than or equal to an upper limit value Vmax (S18). In thecase where the voltage V is greater than or equal to the upper limitvalue Vmax (V≧Vmax), the laser light luminous efficiency is poor and itis necessary to stop the laser oscillation and perform maintenance (forexample, complete gas replacement or the like), and thus the processingof this flowchart may be ended. However, in the case where the voltage Vis not greater than or equal to the upper limit value Vmax (V<Vmax), theprocess may return to S10, where the pulse energy E is stabilized bycontrolling the voltage V and the data of the voltage V is sent to thegas control unit 47.

4.4 Duty Calculation by Laser Control Unit

FIG. 5 is a flowchart illustrating the calculation of an excimer laserapparatus duty according to the first embodiment. The processes shown inFIG. 5 may be carried out by the laser control unit 30 (FIG. 1)independent from the gas control shown in FIG. 3. In the processingshown in FIG. 5, a ratio of a maximum repetition rate of the excimerlaser apparatus relative to the overall repetition rate during laseroscillation may be calculated as the duty D. Although the processesshown in FIG. 5 are carried out separately from the gas control shown inFIG. 3, the following descriptions assume that the gas control can be aprerequisite.

First, the laser control unit 30 may load a pulse number Np0 in a setamount of time Tmax for the case where the excimer laser apparatusoscillates at the maximum repetition rate (S20).

Next, the laser control unit 30 may set a counter N for counting a laserlight pulse number to 0 (S21).

Next, the laser control unit 30 may set a timer T for measuring thelaser light pulse number in a set amount of time and start themeasurement (S22).

Next, the laser control unit 30 may determine whether or not a laserpulse has been outputted (S23). The laser pulse may be a single pulse oflaser light. The determination as to whether or not a laser pulse hasbeen outputted may, for example, be determined based on whether or notdata of the pulse energy E has been received from the optical sensormodule 17. In the case where the laser pulse has not been outputted(S23: NO), the determination may be repeated until the laser pulse isoutputted.

In the case where the laser pulse has been outputted (S23: YES), thelaser control unit 30 may add 1 to the counter N (S24).

Next, the laser control unit 30 may determine whether or not the timer Thas reached the set amount of time Tmax (S25). In the case where the setamount of time Tmax has not been reached (Tmax>T), the process mayreturn to the aforementioned S23, and the pulse number may be measuredby the counter N until the set amount of time Tmax has been reached.

In the case where the set amount of time Tmax has been reached (Tmax≦T),the laser control unit 30 may store the value of the counter N in astorage device as a pulse number Np for the set amount of time Tmax(S26).

Next, the laser control unit 30 may calculate the value of (Np/Np0) asthe duty D (S27). In the case where the value of the duty D is themaximum value of 1, this can indicate that the excimer laser apparatusis oscillating at the maximum repetition rate. The value of the duty Dmay be sent from the laser control unit 30 to the gas control unit 47.

Next, the laser control unit 30 may determine whether or not to stop thecalculation of the duty D (S28). In the case where the calculation is tobe stopped, the process illustrated in this flowchart may end. However,in the case where the calculation is not to be stopped, the process mayreturn to the aforementioned S21.

4.5 Calculation of Gas Control Interval (Details of S300)

FIG. 6A is a flowchart illustrating a first example of a process thatcalculates a gas control interval, indicated in FIG. 3. The processesshown in FIG. 6A may be carried out by the gas control unit 47 as asubroutine of S300, shown in FIG. 3.

As described above, if laser light is outputted for a long period oftime, the halogen gas within the laser chamber 10 can progressivelydecrease; accordingly, the halogen gas filling control may be carriedout each time a predetermined amount of time has elapsed. Furthermore,if laser light is outputted for a long period of time, the concentrationof impurities within the laser chamber 10 can progressively increase;accordingly, the partial gas replacement control may be carried out eachtime a predetermined amount of time has elapsed.

However, the decrease in halogen gas and increase in the concentrationof impurities can also be influenced by the repetition rate of the laserlight or the duty D (FIG. 5), in addition to the output time of thelaser light. Accordingly, the gas control unit 47 may perform acorrection computation for the predetermined amount of time, through thefollowing process.

First, the gas control unit 47 may load a base value Thi0 of a timeinterval for halogen gas filling control and a base value Tpi0 of a timeinterval for partial gas replacement control (S301).

The gas control unit 47 may then calculate the time interval Thi of thehalogen gas filling control, based on the base value Thi0 of the timeinterval for halogen gas filling control and the duty D of the excimerlaser apparatus, as Thi0/D (S302). The duty D may be a value sent fromthe laser control unit 30.

In addition, the gas control unit 47 may calculate the time interval Tpiof the partial gas replacement control, based on the base value Tpi0 ofthe time interval for partial gas replacement control and the duty D ofthe excimer laser apparatus, as Tpi0/D (S303). The duty D may be a valuesent from the laser control unit 30.

FIG. 6B is a graph illustrating a relationship between the duty of theexcimer laser apparatus and the gas control interval calculated as shownin FIG. 6A. The time interval Thi of the halogen gas filling controlcalculated as shown in FIG. 6A may be shortest when the duty D is 1(that is, when oscillating at the maximum repetition rate), and may be aminimum value Thi0. In the case where the duty D is less than 1, thetime interval Thi of the halogen gas filling control may be a value thatis greater than the base value Thi0.

Likewise, the time interval Tpi of the partial gas replacement controlcalculated as shown in FIG. 6A may be shortest when the duty D is 1(that is, when oscillating at the maximum repetition rate), and may be aminimum value Tpi0. In the case where the duty D is less than 1, thetime interval Tpi for the partial gas replacement control may be a valuethat is greater than the base value Tpi0.

Through this, the halogen gas filling control and the partial gasreplacement control can be carried out at an appropriate timing inaccordance with the duty of the excimer laser apparatus.

FIG. 6C is a flowchart illustrating a second example of a process thatcalculates a gas control interval, indicated in FIG. 3. The processesshown in FIG. 6C may be carried out by the gas control unit 47 as asubroutine of S300, shown in FIG. 3.

As described with reference to FIG. 6A, the decrease in halogen gas andincrease in the concentration of impurities can be influenced by therepetition rate of the laser light or the duty D (FIG. 5). However, adecrease in the halogen gas and an increase in the concentration ofimpurities can also occur even if the laser light is not oscillating.Accordingly, by providing an upper limit value for the gas controlinterval, the gas control interval may be prevented from exceeding theupper limit value in the case where the laser light repetition rate islow.

First, the gas control unit 47 may load the base value Thi0 and aconstant value Thic serving as an upper limit for the time interval forhalogen gas filling control, and the base value Tpi0 and a constantvalue Tpic serving as an upper limit for the time interval for partialgas replacement control (S304).

Next, the gas control unit 47 may load the duty D of the excimer laserapparatus, and may determine whether or not the duty D is greater thanor equal to a constant value (for example, 0.2) (S305).

In the case where the duty D is greater than or equal to the constantvalue (S305: YES), the gas control unit 47 may calculate the timeinterval Thi for the halogen gas filling control as Thi0/D, in the samemanner as shown in FIG. 6A (S306). In addition, the gas control unit 47may calculate the time interval Tpi for the partial gas replacementcontrol as Tpi0/D (S307).

However, in the case where the duty D is not greater than or equal tothe constant value (S305: NO), the gas control unit 47 may take the timeinterval Thi for the halogen gas filling control as the constant valueThic (S308). In addition, the gas control unit 47 may take the timeinterval Tpi for the partial gas replacement control as the constantvalue Tpic (S309).

FIG. 6D is a graph illustrating a relationship between the duty of theexcimer laser apparatus and the gas control interval calculated as shownin FIG. 6C. The time interval Thi of the halogen gas filling controlcalculated as shown in FIG. 6C may be shortest when the duty D is 1, andmay be the minimum value Thi0. In the case where the duty D is less thana constant value (for example, 0.2), the time interval Thi of thehalogen gas filling control may be the constant value Thic.

Likewise, the time interval Tpi of the partial gas replacement controlcalculated as shown in FIG. 6C may be shortest when the duty D is 1, andmay be the minimum value Tpi0. In the case where the duty D is less thana constant value (for example, 0.2), the time interval Tpi of thepartial gas replacement control may be the constant value Tpic.

Through this, the halogen gas filling control and the partial gasreplacement control can be carried out at an appropriate timing even inthe case where the laser light oscillates with an extremely longoscillation interval, the case where the laser light is oscillating witha low duty D, and so on.

FIG. 6E is a flowchart illustrating a third example of a process thatcalculates a gas control interval, indicated in FIG. 3. The processesshown in FIG. 6E may be carried out by the gas control unit 47 as asubroutine of S300, shown in FIG. 3.

First, the gas control unit 47 may load the base value Thi0 of the timeinterval for halogen gas filling control and the constant value Tpic ofthe time interval for partial gas replacement control (S310).

The gas control unit 47 may calculate the time interval Thi of thehalogen gas filling control as Thi0/D, in the same manner as shown inFIG. 6A (S311).

However, the gas control unit 47 may take the time interval Tpi for thepartial gas replacement control as the constant value Tpic (S312).

FIG. 6F is a graph illustrating a relationship between the duty of theexcimer laser apparatus and the gas control interval calculated as shownin FIG. 6E. As shown in FIG. 6F, the partial gas replacement control maybe performed in a constant time interval, with the time interval Thi ofthe halogen gas filling control being dependent on the duty D and thetime interval Tpi of the partial gas replacement control being theconstant value Tpic that is not dependent on the duty D.

4.6 Calculation of Halogen Gas Partial Pressure (Details of S400)

FIG. 7A is a flowchart illustrating a first example of a process thatcalculates a halogen gas partial pressure, indicated in FIG. 3. Theprocesses shown in FIG. 7A may be carried out by the gas control unit 47as a subroutine of S400, shown in FIG. 3.

As described above, a decrease in the halogen gas within the laserchamber 10 can be influenced by the laser light repetition rate or theduty D (FIG. 5). Accordingly, the halogen gas partial pressure may becalculated as follows in order to fill the laser chamber 10 with aproper amount of halogen gas during the halogen gas filling control, orin order to supply the laser chamber 10 with a laser gas having a properhalogen gas concentration during the partial gas replacement control.

First, the gas control unit 47 may load a halogen gas partial pressurePh0 present in the laser chamber 10 immediately following the previoushalogen gas filling control (S401). In the process of S401, there arecases where data of the halogen gas partial pressure Ph0 does not existfor the previous halogen gas filling control, such as immediately afterthe excimer laser apparatus has been installed. In such a case, thehalogen gas partial pressure may be calculated at the soonest completegas replacement based on pressures and exhaust amounts occurring beforeand after first and second laser gas supplies, and the calculatedhalogen gas partial pressure may be substituted for Ph0.

Next, the gas control unit 47 may calculate the halogen gas partialpressure Ph as Ph0−k·Np, based on the halogen gas partial pressure Ph0present immediately following the previous halogen gas filling control,the oscillation pulse number Np during a set amount of time (FIG. 5),and a proportionality constant k (S402).

FIG. 7B is a flowchart illustrating a second example of a process thatcalculates the halogen gas partial pressure, indicated in FIG. 3. Theprocesses shown in FIG. 7B may be carried out by the gas control unit 47as a subroutine of S400, shown in FIG. 3.

A decrease in the halogen gas within the laser chamber 10 can also beinfluenced by the time interval Thi of the halogen gas filling control,in addition to the laser light repetition rate or the duty D.Accordingly, the halogen gas partial pressure may be calculated asfollows in order to fill a proper amount of halogen gas during thehalogen gas filling control, or in order to supply a laser gas having aproper halogen gas concentration during the partial gas replacementcontrol.

First, the gas control unit 47 may load a halogen gas partial pressurePh0 present in the laser chamber 10 immediately following the previoushalogen gas filling control (S401).

Next, the gas control unit 47 may calculate the halogen gas partialpressure Ph as Ph0−h·Thi−k·Np, based on the halogen gas partial pressurePh0 present immediately following the previous halogen gas fillingcontrol, the oscillation pulse number Np during a set amount of time,the time interval Thi of the halogen gas filling control, andproportionality constants h and k (S403).

FIG. 7C is a flowchart illustrating a third example of a process thatcalculates the halogen gas partial pressure, indicated in FIG. 3. Theprocesses shown in FIG. 7C may be carried out by the gas control unit 47as a subroutine of S400, shown in FIG. 3.

A decrease in the halogen gas within the laser chamber 10 can also beinfluenced by the voltage V applied between the pair of electrodes 11 aand 11 b, in addition to the laser light repetition rate or the duty D.Accordingly, the halogen gas partial pressure may be calculated asfollows in order to fill a proper amount of halogen gas during thehalogen gas filling control, or in order to supply a laser gas having aproper halogen gas concentration during the partial gas replacementcontrol.

First, the gas control unit 47 may load a halogen gas partial pressurePh0 present in the laser chamber 10 immediately following the previoushalogen gas filling control (S401).

Next, the gas control unit 47 may calculate the halogen gas partialpressure Ph as Ph0−g·Np·f(V), based on the halogen gas partial pressurePhD present immediately following the previous halogen gas fillingcontrol, the oscillation pulse number Np during a set amount of time,the voltage V applied between the pair of electrodes 11 a and 11 b, anda proportionality constant g (S404). Here, f(V) may be (c·V²), or may be(a·V+b). In addition, a, b, and c may be constants. Alternatively, a, b,and c may be functions based on data obtained through experimentation.

4.7 Calculation of Gas Replacement Amount (Details of S500)

FIG. 8A is a flowchart illustrating a first example of a process thatcalculates a gas replacement amount, indicated in FIG. 3. The processesshown in FIG. 8A may be carried out by the gas control unit 47 as asubroutine of S500, shown in FIG. 3. The gas replacement amount may becalculated as follows in order to replace an appropriate amount of gasduring the partial gas replacement control.

First, the gas control unit 47 may load the gas pressure P presentwithin the laser chamber 10 as received from the pressure sensor 16(S501).

Next, the gas control unit 47 may compare the gas pressure P presentwithin the laser chamber 10 with a first threshold Pmin and a secondthreshold Pmax (S502). The first threshold Pmin and the second thresholdPmax may be held in the gas control unit 47 in advance.

In the case where the gas pressure P is lower than the first thresholdPmin (P<Pmin), the gas control unit 47 may set the gas replacementamount Q to a minimum value Qmin (S503).

In the case where the gas pressure P is greater than the secondthreshold Pmax, which is itself greater than the first threshold(Pmin<Pmax<P), the gas control unit 47 may set the gas replacementamount Q to a maximum value Qmax (S504).

However, in the case where the gas pressure P is a value that is betweenthe first threshold Pmin and the second threshold Pmax (Pmin≦P≦Pmax),the gas control unit 47 may set the gas replacement amount Q to a valuethat continuously changes between the minimum value Qmin and the maximumvalue Qmax in accordance with the gas pressure P. For example, the gasreplacement amount Q may be a value expressed by a·P+b, where a and bare constants (S505).

FIG. 8B is a graph illustrating a relationship between the gas pressurein a laser chamber and the gas replacement amount calculated as shown inFIG. 8A. The gas pressure P within the laser chamber 10 can, asdescribed above, increase in the case where the gas pressure has beenraised through the gas pressure control (S600) when the voltage Vapplied between the pair of electrodes 11 a and 11 b is high. In otherwords, the gas pressure P within the laser chamber 10 can rise in thecase where impurities have increased within the laser chamber 10 and theluminous efficiency of the laser light has dropped.

Accordingly, as shown in FIG. 8B, impurities within the laser chamber 10can be reduced by increasing the gas replacement amount Q in the casewhere the gas pressure P within the laser chamber 10 is high.Conversely, the gas replacement amount Q can be reduced in the casewhere the gas pressure P within the laser chamber 10 is low.

FIG. 8C is a flowchart illustrating a second example of a process thatcalculates a gas replacement amount, indicated in FIG. 3. The processesshown in FIG. 8C may be carried out by the gas control unit 47 as asubroutine of S500, shown in FIG. 3. The gas replacement amount may becalculated as follows in order to replace a correct amount of gas duringthe partial gas replacement control.

First, the gas control unit 47 may load the duty D of the excimer laserapparatus received from the laser control unit 30 (S506).

Next, the gas control unit 47 may compare the duty D of the excimerlaser apparatus with a first threshold Dmin and a second threshold Dmax(S507). The first threshold Dmin and the second threshold Dmax may beheld in the gas control unit 47 in advance.

In the case where the duty D is lower than the first threshold Dmin(D<Dmin), the gas control unit 47 may set the gas replacement amount Qto the maximum value Qmax (S508).

However, in the case where the duty D is greater than the secondthreshold Dmax, which is itself greater than the first threshold(Dmin<Dmax<D), the gas control unit 47 may set the gas replacementamount Q to the minimum value Qmin (S509).

In the case where the duty D is a value that is between the firstthreshold Dmin and the second threshold Dmax (Dmin≦D≦Dmax), the gascontrol unit 47 may set the gas replacement amount Q to a value thatcontinuously changes between the minimum value Qmin and the maximumvalue Qmax in accordance with the duty D. For example, the gasreplacement amount Q may be a value expressed by a·D+b, where a and bare constants (S510).

FIG. 8D is a graph illustrating an example of a relationship between theduty of the excimer laser apparatus and the gas replacement amountcalculated as shown in FIG. 8C. In this manner, the gas replacementamount Q may be set based on the duty D of the excimer laser apparatus.

4.8 Gas Pressure Control (Details of S600)

FIG. 9 is a flowchart illustrating the gas pressure control indicated inFIG. 3. The processes shown in FIG. 9 may be carried out by the gascontrol unit 47 as a subroutine of S600, shown in FIG. 3.

First, the gas control unit 47 may store the gas pressure P within thelaser chamber 10 as a pre-control gas pressure Pin in the storage device(S601). The gas pressure P may be received from the pressure sensor 16.

Next, the gas control unit 47 may determine whether or not the voltage Vsupplied between the pair of electrodes 11 a and 11 b is greater thanthe first threshold VH (S602). In the case where the voltage V isgreater than the first threshold VH (S602: YES), the gas control unit 47may carry out the control from S603 to S607, for supplying the secondlaser gas to the laser chamber 10. In the case where the voltage V isnot greater than the first threshold VH (S602: NO), the process maytransit to S608.

In the case where the voltage V is greater than the first threshold VH(S602: YES), the gas control unit 47 may set a value obtained by addinga gas pressure fluctuation amount ΔP to the pre-control gas pressure Pin(Pin+ΔP) as a first target gas pressure Pt1 (S603).

Next, the gas control unit 47 may supply the second laser gas to theinterior of the laser chamber 10 by opening the second laser gasinjection valve B-V and the control valve C-V (S604). The flow rate ofthe second laser gas may be controlled by the mass flow controllerB-MFC. As described above, a mixed gas that is a mixture of argon andneon may be used as the second laser gas. By supplying the second lasergas, which does not contain halogen gas, to the interior of the laserchamber 10, it is possible to suppress a fluctuation in the halogen gaspressure within the laser chamber 10. In other words, aside from raisingthe gas pressure P within the laser chamber 10, fluctuations in theoscillation conditions of the laser light can be suppressed, which makesit possible to ensure the stability of the performance of the excimerlaser apparatus.

Next, the gas control unit 47 may newly load the gas pressure P withinthe laser chamber 10 (S605). Next, the gas control unit 47 may determinewhether or not the newly-loaded gas pressure P has reached the firsttarget gas pressure Pt1 (S606). In the case where the gas pressure P hasnot reached the first target gas pressure Pt1 (Pt1>P), the process mayreturn to the aforementioned S605 with the second laser gas injectionvalve B-V remaining open, and may stand by until the first target gaspressure Pt1 is reached. In the case where the gas pressure P hasreached the first target gas pressure Pt1 (Pt1≦P), the gas control unit47 may close the control valve C-V and the second laser gas injectionvalve B-V (S607).

In the case where the voltage V supplied between the pair of electrodes11 a and 11 b is not greater than the first threshold VH (S602: NO), thegas control unit 47 may determine whether or not the voltage V is lowerthan the second threshold VL (S608). Here, based on the results of thedeterminations in S590 of the main flow and S602 of the presentsubroutine, V<VL may already hold true at the point in time where theprocess has moved to S608. In this case, the determination of YES inS608 may be omitted. In the case where the voltage V is lower than thesecond threshold VL (S608: YES), the gas control unit 47 may partiallyexhaust the gas from within the laser chamber 10 in S609 through S620.In the case where the voltage V is not lower than the second thresholdVL (S608: NO), the control of S609 through S620 need not be carried out.In other words, in the case where the voltage V supplied between thepair of electrodes 11 a and 11 b is within the range from the firstthreshold VH to the second threshold VL, the gas pressure control neednot be started.

In the case where the voltage V is less than the second threshold VL(S608: YES), the gas control unit 47 may set a value obtained bysubtracting the gas pressure fluctuation amount ΔP from the pre-controlgas pressure Pin (Pin−ΔP) as a second target gas pressure Pt2 (S609). Atthis time, the gas control unit 47 may simultaneously start the exhaustpump 46 and open the control valve C-V.

Next, the gas control unit 47 may partially exhaust the gas from withinthe laser chamber 10 by opening the exhaust valve EX-V for apredetermined amount of time and then closing the exhaust valve EX-V(S610).

Next, the gas control unit 47 may newly load the gas pressure P withinthe laser chamber 10 (S611). Next, the gas control unit 47 may determinewhether or not the newly-loaded gas pressure P has reached the secondtarget gas pressure Pt2 (S612). In the case where the gas pressure P hasnot reached the second target gas pressure Pt2 (Pt2<P), the process mayreturn to the aforementioned S610, and the partial exhaust of the gasfrom within the laser chamber 10 may be repeated until the second targetgas pressure Pt2 is reached. In the case where the gas pressure P hasreached the second target gas pressure Pt2 (Pt2≧P), the gas control unit47 may calculate a reduction amount ΔPhex for the halogen gas partialpressure resulting from the gas exhaust (S620). At this time, the gascontrol unit 47 may simultaneously close the control valve C-V and stopthe exhaust pump 46.

FIG. 10 is a flowchart illustrating a process for calculating thereduction amount for the halogen gas partial pressure indicated in FIG.9. When the gas pressure is reduced through the control carried out inS609 through S612 of FIG. 9, the halogen gas partial pressure within thelaser chamber 10 can decrease. Accordingly, the gas control unit 47 may,through the following processing, calculate the reduction amount ΔPhexof the halogen gas partial pressure.

First, the gas control unit 47 may load the halogen gas partial pressurePh calculated in the aforementioned S400 (FIG. 3), and may store thehalogen gas partial pressure Ph in the storage device as a pre-controlhalogen gas partial pressure Phin (S621).

Next, the gas control unit 47 may calculate the reduction amount ΔPhexof the halogen gas partial pressure as ΔP·Phin/Pin, using the gaspressure fluctuation amount ΔP resulting from the gas pressure control,the pre-control halogen gas partial pressure Phin, and the pre-controlgas pressure Pin (S622).

Note that after the process of S620 shown in FIG. 10 ends, theprocessing may return to S200 in FIG. 3, and the halogen gas partialpressure Ph may be recalculated in S400. At this time, the halogen gaspartial pressure Ph may be recalculated by subtracting the reductionamount ΔPhex from the halogen gas partial pressure calculated in FIG.10. The halogen gas filling control (S700) may be carried out using thehalogen gas partial pressure Ph found in this manner.

FIG. 11A is a graph illustrating changes in the gas pressure within thelaser chamber and a voltage applied between the electrodes resultingfrom the opening/closing of a second laser gas injection valve, asindicated in FIG. 9.

In the case where the voltage V supplied between the pair of electrodes11 a and 11 b is within the range from the first threshold VH to thesecond threshold VL, the gas pressure control is not started; however,as shown in FIG. 11A, the gas pressure control can start if the voltageV exceeds the first threshold VH. In the case where the voltage V hasexceeded the first threshold VH, the second laser gas injection valveB-V is opened as a result of the gas pressure control, and the gaspressure P within the laser chamber 10 can increase gradually from thepre-control gas pressure Pin. The output of the excimer laser apparatusalso tends to increase when the gas pressure P within the laser chamber10 increases, and thus the voltage V can be decreased through theprocessing shown in FIG. 4 in order to make the output of the excimerlaser apparatus constant. The second laser gas injection valve B-V isclosed when the gas pressure P within the laser chamber 10 reaches thefirst target gas pressure Pt1; the increase in the gas pressure P thusstops, which in turn can also stop the decrease in the voltage V.

In this manner, an excessive increase in the voltage V supplied betweenthe pair of electrodes 11 a and 11 b can be suppressed by increasing thegas pressure P within the laser chamber 10.

FIG. 11B is a graph illustrating changes in the gas pressure within thelaser chamber and the voltage applied between electrodes resulting fromthe opening/closing of the exhaust valve, indicated in FIG. 9.

In the case where the voltage V supplied between the pair of electrodes11 a and 11 b is within the range from the first threshold VH to thesecond threshold VL, the gas pressure control is not started; however,as shown in FIG. 11B, the gas pressure control can start if the voltageV is less than the second threshold VL. In the case where the voltage Vhas become less than the second threshold VL, the exhaust valve EX-V isopened for a predetermined amount of time and is then closed as a resultof the gas pressure control, and thus the gas pressure P within thelaser chamber 10 can decrease slightly from the pre-control gas pressurePin. The output of the excimer laser apparatus also tends to decreasewhen the gas pressure P within the laser chamber 10 decreases, and thusthe voltage V can be increased through the processing shown in FIG. 4 inorder to make the output of the excimer laser apparatus constant.

The opening/closing operations of the exhaust valve EX-V are repeateduntil the gas pressure P within the laser chamber 10 reaches the secondtarget gas pressure Pt2, and with each repetition, the gas pressure Pwithin the laser chamber 10 can decrease slightly, and the voltage V canincrease slightly. The opening/closing operations of the exhaust valveEX-V is ended when the gas pressure P within the laser chamber 10reaches the second target gas pressure Pt2; the decrease in the gaspressure P thus stops, which in turn can also stop the increase in thevoltage V.

In this manner, an excessive decrease in the voltage V supplied betweenthe pair of electrodes 11 a and 11 b can be suppressed by decreasing thegas pressure P within the laser chamber 10.

4.9 Halogen Gas Filling Control (Details of S700)

FIG. 12 is a flowchart illustrating the halogen gas filling controlindicated in FIG. 3. The processes shown in FIG. 12 may be carried outby the gas control unit 47 as a subroutine of S700, shown in FIG. 3.

First, the gas control unit 47 may load the halogen gas partial pressurePh, the gas pressure P, and a target halogen gas partial pressure Pht(S701). The halogen gas partial pressure Ph may be that which wascalculated in the aforementioned S400 (FIG. 3). The gas pressure P maybe received from the pressure sensor 16. The target halogen gas partialpressure Pht may be a value that is set in accordance with operationalconditions of the excimer laser apparatus.

Next, the gas control unit 47 may store the gas pressure P as thepre-control gas pressure Pin in the storage device (S702). Next, the gascontrol unit 47 may calculate a first laser gas injection amount ΔPf2for controlling the halogen gas partial pressure within the laserchamber 10 to the target halogen gas partial pressure Pht (S710).Details of this calculation process will be provided later.

Next, the gas control unit 47 may set a value obtained by adding thefirst laser gas injection amount ΔPf2 to the pre-control gas pressurePin (Pin+ΔPf2) as a target gas pressure Px present following the firstlaser gas injection (prior to exhaust) (S720). Next, the gas controlunit 47 may supply the first laser gas to the interior of the laserchamber 10 by opening the first laser gas injection valve F2-V and thecontrol valve C-V (S721). The flow rate of the first laser gas may becontrolled by the mass flow controller F2-MFC. As described above, amixed gas that is a mixture of argon, neon, and fluorine may be used asthe first laser gas. The halogen gas partial pressure within the laserchamber 10 can be increased by supplying the first laser gas, whichincludes fluorine gas, to the interior of the laser chamber 10.

Next, the gas control unit 47 may newly load the gas pressure P withinthe laser chamber 10 (S722). Next, the gas control unit 47 may determinewhether or not the newly-loaded gas pressure P has reached the targetgas pressure Px present following the first laser gas injection (S723).In the case where the gas pressure P has not reached the target gaspressure Px (Px>P), the process may return to the aforementioned S722with the first laser gas injection valve F2-V remaining open, and maystand by until the target gas pressure Px is reached. In the case wherethe gas pressure P has reached the target gas pressure Px (Px≦P), thegas control unit 47 may close the control valve C-V and the first lasergas injection valve F2-V (S724). After this, the gas control unit 47 maystart the exhaust pump 46 and open the control valve C-V. At this time,the exhaust valve EX-V may be closed.

Next, the gas control unit 47 may partially exhaust the gas from withinthe laser chamber 10 by opening the exhaust valve EX-V for apredetermined amount of time and then closing the exhaust valve EX-V(S725).

Next, the gas control unit 47 may newly load the gas pressure P withinthe laser chamber 10 (S726). Next, the gas control unit 47 may determinewhether or not the newly-loaded gas pressure P has returned to thepre-control gas pressure Pin (S727). In the case where the gas pressureP has not returned to the pre-control gas pressure Pin (Pin<P), theprocess may return to the aforementioned S725, and the partial exhaustof gas from within the laser chamber 10 may be repeated until the gaspressure P returns to the pre-control gas pressure Pin. During thisperiod, the exhaust pump 46 may be running, and the control valve C-Vmay be in an open state. In the case where the gas pressure P hasreturned to the pre-control gas pressure Pin (Pin≧P), the gas controlunit 47 may close the control valve C-V and stop the exhaust pump 46.The processing of this flowchart may then end.

FIG. 13 is a flowchart illustrating a process for calculating the firstlaser gas injection amount indicated in S710 of FIG. 12. The gas controlunit 47 may, through the following processing, calculate the first lasergas injection amount ΔPf2.

First, the gas control unit 47 may store the halogen gas partialpressure Ph calculated in the aforementioned S400 (FIG. 3) in thestorage device as the pre-control halogen gas partial pressure Phin(S711).

Next, the gas control unit 47 may load a halogen gas concentration(volume ratio) C0 in the first laser gas (S712). The halogen gasconcentration in the first laser gas may be a halogen gas concentration(volume ratio) in the first receptacle F2, or may be inputted into thegas control unit 47 in advance and held so as to be capable of beingreferred to by the gas control unit 47.

A halogen gas partial pressure increase amount ΔPh in the case where thefirst laser gas is injected into the laser chamber 10 (by the injectionamount ΔPf2) can be expressed by the following equation.

ΔPh=C0·ΔPf2

The halogen gas partial pressure that has decreased due to exhausting tothe pre-control gas pressure Pin (an exhaust amount equivalent to theinjection amount ΔPf2) after the first laser gas has been injected intothe laser chamber 10 (that is, a reduction amount ΔPhex) can beexpressed by the following equation.

ΔPhex=ΔPf2·(Phin+C0·ΔPf2)/(Pin+ΔPf2)  Formula 1

Meanwhile, the target halogen gas partial pressure Pht can be expressedby the following equation.

Pht=Phin+C0·ΔPf2−ΔPhex  Formula 2

Accordingly, the gas control unit 47 may calculate a APf2 that fulfillsFormulas 1 and 2 as the first laser gas injection amount ΔPf2 (S713).Alternatively, the gas control unit 47 may hold a table or the like inadvance, and may determine the first laser gas injection amount ΔPf2 byreferring to this table. The table may hold values for the first lasergas injection amount ΔPf2 that correspond to, for example, the gaspressure P, the halogen gas partial pressure Ph, the target halogen gaspartial pressure Pht, or the like.

FIG. 14 is a graph illustrating changes in the gas pressure within thelaser chamber resulting from the halogen gas filling control indicatedin FIG. 12. The gas control unit 47 may start the halogen gas fillingcontrol each time the time interval Thi of the halogen gas fillingcontrol passes. When the halogen gas filling control is started, thefirst laser gas injection valve F2-V and the control valve C-V areopened, and the gas pressure P within the laser chamber 10 can increasegradually from the pre-control gas pressure Pin. When the gas pressure Pwithin the laser chamber 10 reaches the target gas pressure Px, thecontrol valve C-V and the first laser gas injection valve F2-V areclosed, and thus the increase in the gas pressure P can be stopped.

Next, the exhaust pump 46 is started, and after the control valve C-V isopened, the exhaust valve EX-V is opened for a predetermined amount oftime and then closed; as a result, the gas pressure P within the laserchamber 10 can decrease slightly from the target gas pressure Px. Theopening/closing operations of the exhaust valve EX-V are repeated untilthe gas pressure P within the laser chamber 10 reaches the pre-controlgas pressure Pin, and with each repetition, the gas pressure P withinthe laser chamber 10 can decrease slightly. The opening/closingoperations of the exhaust valve EX-V end when the gas pressure P withinthe laser chamber 10 reaches the pre-control gas pressure Pin; thus thedecrease in the gas pressure P can stop. Thereafter, the control valveC-V may be closed and the exhaust pump 46 may be stopped.

In this manner, the halogen gas may be supplied to the interior of thelaser chamber 10, and the gas pressure P within the laser chamber 10 maythen be returned to a value that is close to the pre-control gaspressure Pin. Accordingly, in the halogen gas filling control,fluctuations in the oscillation conditions of the laser light can besuppressed, which makes it possible to ensure the stability of theperformance of the excimer laser apparatus, even while the halogen gaspartial pressure within the laser chamber 10 is increased.

4.10 Partial Gas Replacement Control (Details of S800)

FIG. 15 is a flowchart illustrating the partial gas replacement controlindicated in FIG. 3. The processes shown in FIG. 15 may be carried outby the gas control unit 47 as a subroutine of S800, shown in FIG. 3.

First, the gas control unit 47 may load the gas replacement amount Q,the gas pressure P, and the halogen gas partial pressure Ph (S801). Thegas replacement amount Q may be that calculated in the aforementionedS500 (FIG. 3). The gas pressure P may be received from the pressuresensor 16. The halogen gas partial pressure Ph may be calculated in theaforementioned S400 (FIG. 3).

Next, the gas control unit 47 may store the gas pressure P as thepre-control gas pressure Pin in the storage device (S802). Next, the gascontrol unit 47 may calculate the first laser gas injection amount ΔiPf2and a second laser gas injection amount ΔPb for the partial gasreplacement control (S810). Details of this calculation process will beprovided later.

Next, the gas control unit 47 may set a value obtained by adding thefirst laser gas injection amount ΔPf2 to the pre-control gas pressurePin (Pin+ΔPf2) as a first target gas pressure Px1 present following thefirst laser gas injection (S820). Next, the gas control unit 47 maysupply the first laser gas to the interior of the laser chamber 10 byopening the first laser gas injection valve F2-V and the control valveC-V (S821). The flow rate of the first laser gas may be controlled bythe mass flow controller F2-MFC. As described above, a mixed gas that isa mixture of argon, neon, and fluorine may be used as the first lasergas. Through this, the first laser gas, which contains fluorine gas, canbe supplied to the interior of the laser chamber 10.

Next, the gas control unit 47 may newly load the gas pressure P withinthe laser chamber 10 (S822). Next, the gas control unit 47 may determinewhether or not the newly-loaded gas pressure P has reached the firsttarget gas pressure Px1 present following the first laser gas injection(S823). In the case where the gas pressure P has not reached the firsttarget gas pressure Px1 (Px1>P), the process may return to theaforementioned S822 with the first laser gas injection valve F2-Vremaining open, and may stand by until the first target gas pressure Px1is reached. In the case where the gas pressure P has reached the firsttarget gas pressure Px1 (Px1≦P), the gas control unit 47 may close thecontrol valve C-V and the first laser gas injection valve F2-V (S824).

Next, the gas control unit 47 may set a value obtained by adding thefirst laser gas injection amount ΔPf2 and the second laser gas injectionamount ΔPb to the pre-control gas pressure Pin (Pin+ΔPf2+ΔPb) as asecond target gas pressure Px2 present following the second laser gasinjection (S825). Next, the gas control unit 47 may supply the secondlaser gas to the interior of the laser chamber 10 by opening the secondlaser gas injection valve B-V and the control valve C-V (S826). The flowrate of the second laser gas may be controlled by the mass flowcontroller B-MFC. As described above, a mixed gas that is a mixture ofargon and neon may be used as the second laser gas. By properlycalculating the first laser gas injection amount ΔPf2 and the secondlaser gas injection amount ΔPb (S810), the halogen gas partial pressurewithin the laser chamber 10 may be prevented from fluctuating betweenbefore and after the partial gas replacement control is carried out.

Next, the gas control unit 47 may newly load the gas pressure P withinthe laser chamber 10 (S827). Next, the gas control unit 47 may determinewhether or not the newly-loaded gas pressure P has reached the secondtarget gas pressure Px2 present following the second laser gas injection(S828). In the case where the gas pressure P has not reached the secondtarget gas pressure Px2 (Px2>P), the process may return to theaforementioned S827 with the second laser gas injection valve B-Vremaining open, and may stand by until the second target gas pressurePx2 is reached. In the case where the gas pressure P has reached thesecond target gas pressure Px2 (Px2≦P), the gas control unit 47 mayclose the control valve C-V and the second laser gas injection valve B-V(S829). After this, the gas control unit 47 may start the exhaust pump46 and open the control valve C-V. At this time, the exhaust valve EX-Vmay be closed.

Next, the gas control unit 47 may partially exhaust the gas from withinthe laser chamber 10 by opening the exhaust valve EX-V for apredetermined amount of time and then closing the exhaust valve EX-V(S830).

Next, the gas control unit 47 may newly load the gas pressure P withinthe laser chamber 10 (S831). Next, the gas control unit 47 may determinewhether or not the newly-loaded gas pressure P has returned to thepre-control gas pressure Pin (S832). In the case where the gas pressureP has not returned to the pre-control gas pressure Pin (Pin<P), theprocess may return to the aforementioned S830, and the partial exhaustof gas from within the laser chamber 10 may be repeated until the gaspressure P returns to the pre-control gas pressure Pin. During thisperiod, the exhaust pump 46 may be running, and the control valve C-Vmay be in an open state. In the case where the gas pressure P hasreturned to the pre-control gas pressure Pin (Pin≧P), the gas controlunit 47 may close the control valve C-V and stop the exhaust pump 46.The processing of this flowchart may then end.

FIG. 16 is a flowchart illustrating processes for calculating the firstlaser gas injection amount and the second laser gas injection amountindicated in FIG. 15. The gas control unit 47 may, through the followingprocessing, calculate the first laser gas injection amount ΔPf2 and thesecond laser gas injection amount ΔPb.

First, the gas control unit 47 may store the halogen gas partialpressure Ph calculated in the aforementioned S400 (FIG. 3) in thestorage device as the pre-control halogen gas partial pressure Phin(S811). Next, the gas control unit 47 may load a halogen gasconcentration (volume ratio) C0 in the first laser gas (S812). Thehalogen gas concentration in the first laser gas may be inputted intothe gas control unit 47 in advance and held so as to be capable of beingreferred to by the gas control unit 47.

The gas control unit 47 may calculate a halogen gas concentration(volume ratio) Ch0 within the laser chamber 10 through the followingequation (S813).

Ch0=Phin/Pin

In the case where the halogen gas concentration (volume ratio) in theinjected gas containing both the first laser gas (injection amount ΔPf2,halogen gas concentration C0) and the second laser gas (injection amountΔPb) is equal to the pre-control halogen gas concentration (volumeratio) Ch0, the following equation can hold true.

Ch0=C0·ΔPf2/(ΔPf2+ΔPb)  Formula 3

Meanwhile, the gas replacement amount Q can be expressed through thefollowing equation.

Q=ΔPf2+ΔPb  Formula 4

Accordingly, the gas control unit 47 may calculate a ΔPf2 and a ΔPb thatfulfill Formulas 3 and 4 as the first laser gas injection amount ΔPf2and the second laser gas injection amount ΔPb (S814).

FIG. 17 is a graph illustrating changes in the gas pressure within thelaser chamber resulting from the partial gas replacement controlindicated in FIG. 15. The gas control unit 47 may start the partial gasreplacement control each time the time interval Tpi of the partial gasreplacement control passes. When the partial gas replacement control isstarted, the first laser gas injection valve F2-V and the control valveC-V are opened, and the gas pressure P within the laser chamber 10 canincrease gradually from the pre-control gas pressure Pin. When the gaspressure P within the laser chamber 10 reaches the first target gaspressure Px1, the control valve C-V and the first laser gas injectionvalve F2-V are closed. Next, the second laser gas injection valve B-Vand the control valve C-V are opened, and thus the gas pressure P withinthe laser chamber 10 can further increase from the first target gaspressure Px1. When the gas pressure P within the laser chamber 10reaches the second target gas pressure Px2, the control valve C-V andthe second laser gas injection valve B-V are closed, and thus theincrease in the gas pressure P can be stopped.

Next, the exhaust pump 46 is started, and after the control valve C-V isopened, the exhaust valve EX-V is opened for a predetermined amount oftime and then closed; as a result, the gas pressure P within the laserchamber 10 can decrease slightly from the second target gas pressurePx2. The opening/closing operations of the exhaust valve EX-V arerepeated until the gas pressure P within the laser chamber 10 reachesthe pre-control gas pressure Pin, and with each repetition, the gaspressure P within the laser chamber 10 can decrease slightly. Theopening/closing operations of the exhaust valve EX-V end when the gaspressure P within the laser chamber 10 reaches the pre-control gaspressure Pin; thus the decrease in the gas pressure P can stop.Thereafter, the control valve C-V may be closed and the exhaust pump 46may be stopped.

As described thus far, the first laser gas injection amount ΔPf2 and thesecond laser gas injection amount ΔPb may be calculated so that thehalogen gas partial pressure does not change between before and afterthe partial gas replacement control. Furthermore, the gas pressurewithin the laser chamber 10 may be almost entirely prevented fromchanging between before and after the partial gas replacement control byexhausting essentially the same amount as the total injection amounts ofthe first laser gas and the second laser gas. Accordingly, fluctuationsin the oscillation conditions of the laser light can be suppressed,which makes it possible to ensure the stability of the performance ofthe excimer laser apparatus, while at the same time reducing theconcentration of impurities.

In addition, because the second laser gas is supplied to the interior ofthe laser chamber 10 after the first laser gas has been supplied to theinterior of the laser chamber 10, halogen gas that remains in the firstpipe 41, which is a shared pipe, can be pushed into the laser chamber 10by the second laser gas. Accordingly, the halogen gas partial pressurewithin the laser chamber 10 can be precisely controlled.

5. Second Embodiment Integrated Control Including Partial GasReplacement Control and Halogen Gas Filling Control

5.1 Outline of Gas Control

FIG. 18 is a state transition diagram illustrating gas control accordingto the second embodiment. As shown in FIG. 18, the gas control accordingto the second embodiment may include the gas pressure control (S600) andpartial gas replacement and halogen gas filling control (S840). A gascontrol stopped state (S0) may be included as well. The configuration ofthe excimer laser apparatus may be the same as in the first embodiment.

The partial gas replacement and halogen gas filling control (S840) may,like the partial gas replacement control according to the firstembodiment, inject the first laser gas and the second laser gas into thelaser chamber 10 and exhaust an amount of gas equivalent to the totalinjection amounts of those gases from the laser chamber 10. However, inthe partial gas replacement and halogen gas filling control according tothe second embodiment, the first laser gas injection amount and thesecond laser gas injection amount may be calculated so that the halogengas partial pressure, which has decreased due to laser light output overa long period of time, is restored to a predetermined value.

5.2 Main Flow

FIG. 19 is a flowchart illustrating the gas control according to thesecond embodiment. The processes shown in FIG. 19 may be carried out bythe gas control unit 47 (FIG. 1). The processing shown in FIG. 19 may,in S100, start measuring time using a timer Thp instead of the timers Thand Tp described in the first embodiment. In addition, a gas controlinterval Thpi may be calculated instead of the gas control intervals Thiand Tpi described in the first embodiment (S340). The calculation of thegas control interval Thpi will be described later.

In addition, the processing illustrated in FIG. 19 differs from thatdescribed in the first embodiment in that the partial gas replacementand halogen gas filling control (S840) can be included as a singlestate, instead of the halogen gas filling control and the partial gasreplacement control being included as individual states as in the firstembodiment.

In the second embodiment, in the case where the conditions for gaspressure control are not in place (S590: YES), the gas control unit 47may compare the timer Thp with the time interval Thpi for the partialgas replacement and halogen gas filling control (S791).

In the case where the timer Thp has reached the time interval Thpi ofthe partial gas replacement and halogen gas filling control (Thpi<Thp),the gas control unit 47 may carry out the partial gas replacement andhalogen gas filling control (S840). The details of the partial gasreplacement and halogen gas filling control will be described later.When the partial gas replacement and halogen gas filling control hasended, the timer Thp may be reset (S881). The other processes may be thesame as those described in the first embodiment.

5.3 Calculation of Gas Control Interval (Details of S340)

FIG. 20A is a flowchart illustrating a first example of a process thatcalculates the gas control interval, indicated in FIG. 19. FIG. 20B is agraph illustrating a relationship between the duty of the excimer laserapparatus and the gas control interval calculated as shown in FIG. 20A.

First, the gas control unit 47 may load a base value Thpi0 of a timeinterval for the partial gas replacement and halogen gas filling control(S341).

Next, the gas control unit 47 may calculate the time interval Thpi forthe partial gas replacement and halogen gas filling control as Thpi0/D,based on the loaded base value Thpi0 and the duty D of the excimer laserapparatus (S342).

FIG. 20C is a flowchart illustrating a second example of a process thatcalculates the gas control interval, indicated in FIG. 19. FIG. 20D is agraph illustrating a relationship between the duty of the excimer laserapparatus and the gas control interval calculated as shown in FIG. 20C.

First, the gas control unit 47 may load the base value Thpi0 of the timeinterval for the partial gas replacement and halogen gas filling controland a constant value Thpic serving as an upper limit (S343).

Next, the gas control unit 47 may load the duty D of the excimer laserapparatus, and may determine whether or not the duty D is greater thanor equal to a constant value (for example, 0.2) (S344).

In the case where the duty D is greater than or equal to the constantvalue (S344: YES), the gas control unit 47 may calculate the timeinterval Thpi for the partial gas replacement and halogen gas fillingcontrol as Thpi0/D, in the same manner as shown in FIG. 20A (S345).

However, in the case where the duty D is not greater than or equal tothe constant value (S344: NO), the gas control unit 47 may take the timeinterval Thpi for the partial gas replacement and halogen gas fillingcontrol as the constant value Thpic (S346).

5.4 Partial Gas Replacement and Halogen Gas Filling Control (Details ofS840)

FIG. 21 is a flowchart illustrating partial gas replacement and halogengas filling control indicated in FIG. 19. In the partial gas replacementand halogen gas filling control, the first laser gas and the secondlaser gas may be injected into the laser chamber 10 and an amount of gasequivalent to the total injection amounts of those gases may beexhausted from the laser chamber 10, in the same manner as the partialgas replacement control according to the first embodiment. However, inthe partial gas replacement and halogen gas filling control according tothe second embodiment, the injection amounts of the first laser gas andthe second laser gas may be different from those used in the partial gasreplacement control according to the first embodiment.

The gas control unit 47 may load the gas replacement amount Q, the gaspressure P, the halogen gas partial pressure Ph, and the target halogengas partial pressure Pht (S841). Next, the gas control unit 47 may storethe gas pressure P as the pre-control gas pressure Pin in the storagedevice (S842).

Furthermore, the gas control unit 47 may calculate the first laser gasinjection amount ΔPf2 and the second laser gas injection amount ΔPb forcontrolling the halogen gas partial pressure within the laser chamber 10to the target halogen gas partial pressure Pht (S850) The otherprocesses may be the same as those in the partial gas replacementcontrol according to the first embodiment (FIG. 15).

FIG. 22 is a flowchart illustrating processes for calculating the firstlaser gas injection amount and the second laser gas injection amountindicated in FIG. 21. The gas control unit 47 may, through the followingprocessing, calculate the first laser gas injection amount ΔPf2 and thesecond laser gas injection amount ΔPb.

First, the gas control unit 47 may store the halogen gas partialpressure Ph in the storage device as the pre-control halogen gas partialpressure Phin (S851).

Next, the gas control unit 47 may load the halogen gas concentration C0in the first laser gas (a volume ratio of the halogen component of thefirst laser gas) (S852). The halogen gas concentration in the firstlaser gas may be a halogen gas concentration (volume ratio) in the firstreceptacle F2, or may be inputted into the gas control unit 47 inadvance and held so as to be capable of being referred to by the gascontrol unit 47.

The halogen gas partial pressure increase amount ΔPh in the case wherethe first laser gas (injection amount ΔPf2) and the second laser gas(injection amount ΔPb) are injected into the laser chamber 10 can beexpressed by the following equation.

ΔPh=C0·ΔPf2

The halogen gas partial pressure that decreases due to exhausting to thepre-control gas pressure Pin (an exhaust amount equivalent to theinjection amount ΔPf2+ΔPb) after the first laser gas and the secondlaser gas have been injected into the laser chamber 10 (that is, thereduction amount ΔPhex) can be expressed by the following equation.

ΔPhex=(ΔPf2+ΔPb)·(Phin+C0·ΔPf2)/(Pin+ΔPf2+ΔPb)  Formula 5

Meanwhile, the target halogen gas partial pressure Pht can be expressedby the following equation. Note that the target halogen gas partialpressure Pht may, as in the first embodiment, be a value that is set inaccordance with operational conditions of the excimer laser apparatus.

Pht=Phin+C0−ΔPf2−ΔPhex  Formula 6

Furthermore, the gas replacement amount Q can be expressed through thefollowing equation.

Q=ΔPf2+ΔPb  Formula 7

Accordingly, the gas control unit 47 may calculate a ΔPf2 and a ΔPb thatfulfill Formulas 5 through 7 as the first laser gas injection amountΔPf2 and the second laser gas injection amount ΔPb (S853).Alternatively, the gas control unit 47 may hold a table or the like inadvance, and may determine the first laser gas injection amount ΔPf2 andthe second laser gas injection amount ΔPb by referring to this table.The table may hold values for the first laser gas injection amount ΔPf2and the second laser gas injection amount ΔPb that correspond to, forexample, the gas replacement amount Q, the gas pressure P, the halogengas partial pressure Ph, the target halogen gas partial pressure Pht, orthe like.

According to the second embodiment, impurities within the laser chamber10 can be reduced and the halogen gas partial pressure can be restoredthrough a single process by carrying out the partial gas replacementcontrol and the halogen gas filling control as an integrated process.

6. Third Embodiment MOPO System

6.1 Overall Description of MOPO System

FIG. 23 schematically illustrates the configuration of an excimer lasersystem according to a third embodiment. The excimer laser system mayinclude, in addition to the excimer laser apparatus according to thefirst embodiment: high-reflecting mirrors 18 a and 18 b; a laser chamber20; a pair of electrodes 21 a and 21 b; a charger 22; a pulse powermodule (PPM) 23; a partially-reflecting mirror 24; an output couplingmirror 25; a pressure sensor 26; and an optical sensor module 27.

The laser chamber 10, the pair of electrodes 11 a and 11 b, the charger12, the pulse power module (PPM) 13, the line narrow module 14, and theoutput coupling mirror 15 described in the first embodiment mayconfigure a master oscillator MO. The laser chamber 20, the pair ofelectrodes 21 a and 21 b, the charger 22, the pulse power module (PPM)23, the partially-reflecting mirror 24, and the output coupling mirror25 may configure a power oscillator PO. A MOPO-type excimer laser systemmay be configured by the master oscillator MO and the power oscillatorPO.

Pulsed laser light outputted by the master oscillator MO may enter intothe partially-reflecting mirror 24 of the power oscillator PO via thehigh-reflecting mirrors 18 a and 18 b. The pulsed laser light that hasentered into the partially-reflecting mirror 24 can pass through theinterior of the laser chamber 20 and be amplified while traveling backand forth between the partially-reflecting mirror 24 and the outputcoupling mirror 25. Some of the amplified pulsed laser light can thenpass through the output coupling mirror 25 and be outputted as outputlaser light, and can then be outputted to the exposure device 100 viathe optical sensor module 27.

The configurations and functions of the charger 22, the pulse powermodule (PPM) 23, the pressure sensor 26, the optical sensor module 27,and so on may be the same as the corresponding elements described in thefirst embodiment.

In the gas control device 40, the first pipe 41 that is connected to thelaser chamber 10 is connected to the second through fourth pipes 42through 44. In addition to this, a fifth pipe 45 that is connected tothe laser chamber 20 may also be connected. Accordingly, the laserchamber 20 may be connected to each of the first receptacle F2, thesecond receptacle B, and the exhaust pump 46. A control valve C-V2 maybe provided in the fifth pipe 45.

6.2 Gas Control in MOPO System

FIG. 24 is a state transition diagram illustrating gas control accordingto the third embodiment. As shown in FIG. 24, the gas control accordingto the third embodiment may include gas pressure control (S600 po),halogen gas filling control (S700 po), and partial gas replacementcontrol (S800 po) in the power oscillator PO, in addition to gaspressure control (S600 mo), halogen gas filling control (S700 mo), andpartial gas replacement control (S800 mo) in the master oscillator MO.

It is possible for the timing of the rise of a laser pulse waveform andso on to fluctuate if operational conditions of the excimer laserapparatus, such as the halogen gas partial pressure, are changed.However, a MOPO system is advantageous in that, for example, the energyof the pulsed laser light outputted from the power oscillator PO doesnot easily fluctuate, even if the timing of the rise of the laser pulsewaveform and so on fluctuate in one of the master oscillator MO and thepower oscillator PO. Accordingly, the gas control in the masteroscillator MO and the gas control in the power oscillator PO may becarried out independently in accordance with the states of the gases inthe respective oscillators.

FIG. 25 is a flowchart illustrating the gas control according to thethird embodiment. The processes shown in FIG. 25 may be carried out bythe gas control unit 47 (FIG. 23). The processing shown in FIG. 25 canbe different from that described in the first embodiment in that theprocesses in S300 to S880 in the first embodiment (FIG. 3) are carriedout in both the master oscillator MO and the power oscillator PO. Theprocessing may be the same as that described in the first embodiment inother respects.

7. Fourth Embodiment Integration of Control in MOPO System

FIG. 26 is a state transition diagram illustrating gas control accordingto the fourth embodiment. FIG. 27 is a flowchart illustrating the gascontrol according to the fourth embodiment.

The gas control according to the fourth embodiment can differ from thatin the third embodiment in that the partial gas replacement control andthe halogen gas filling control performed in the master oscillator MOare integrated and the partial gas replacement control and the halogengas filling control performed in the power oscillator PO are integrated.The processing may be the same as that described in the third embodimentin other respects. The details of a partial gas replacement and halogengas filling control that integrates the partial gas replacement controland the halogen gas filling control may be the same as in the secondembodiment.

8. Fifth Embodiment Integration of Chargers in MOPO System

FIG. 28 schematically illustrates the configuration of an excimer lasersystem according to a fifth embodiment. As shown in FIG. 28, the pair ofelectrodes 11 a and 11 b included in the master oscillator MO and thepair of electrodes 21 a and 21 b included in the power oscillator PO maybe connected to a shared charger 12. The configuration may be the sameas that described in the fourth embodiment in other respects.

In the case where the charger 12 that is shared by the master oscillatorMO and the power oscillator PO is used, voltage control can be carriedout in common for the pair of electrodes 11 a and 11 b and the pair ofelectrodes 21 a and 21 b. In other words, even if the pulse energy oflaser light has changed in one of the laser chambers due to an increasein the concentration of impurities or the like, the voltage control iscarried out in common for both, and thus the output energy of the poweroscillator PO can be stabilized. As a result, even if an attempt is madeto carry out the gas pressure control based on the voltage applied tothe electrodes, there are cases where which of the master oscillator MOand the power oscillator PO should carry out the gas pressure controlcannot be determined precisely based only on the voltage. Accordingly,which of the master oscillator MO and the power oscillator PO shouldcarry out the gas pressure control may be determined by detecting theoutput energy of the master oscillator MO.

FIG. 29 is a flowchart illustrating the gas control according to thefifth embodiment. The gas control unit 47 may load the voltage V, theduty D, a gas pressure Pmo of the master oscillator MO, a gas pressurePpo of the power oscillator PO, and a pulse energy Emo of the masteroscillator MO (S210).

In addition, the gas control unit 47 may compare the voltage V with thefirst threshold VH and the second threshold VL (S591, S594). In the casewhere the voltage V is not within the range from the first threshold VHto the second threshold VL (S591: YES or S594: YES), it can bedetermined that gas pressure control should be carried out in the laserchamber of the master oscillator MO, the power oscillator PO, or both.Accordingly, the gas control unit 47 may compare the pulse energy Emo ofthe master oscillator MO with a first threshold Emomin and a secondthreshold Emomax (S592, S593, 5595, S596).

In the case where the comparison results in relationships where VL<VH<Vand Emo<Emomin<Emomax (S592: YES), it can be understood that the outputof the master oscillator MO is low and the output of the poweroscillator PO cannot be ensured unless a high voltage is applied betweenthe electrodes of the master oscillator MO and the power oscillator PO.Accordingly, in this case, the second laser gas may be injected into thelaser chamber 10 of the master oscillator MO (S602 mo).

Meanwhile, in the case where relationships where VL<VH<V andEmomin<Emomax<Emo are present (S593: YES), it can be understood that theamplification rate of the power oscillator PO is low and the output ofthe power oscillator PO cannot be ensured unless a high voltage isapplied between the electrodes of the master oscillator MO and the poweroscillator PO. Accordingly, in this case, the second laser gas may beinjected into the laser chamber 20 of the power oscillator PO (S602 po).

Meanwhile, in the case where relationships where V<VL<VH andEmomin<Emomax<Emo are present (S595: YES), it can be understood that theoutput of the master oscillator MO is excessive and the output of thepower oscillator PO will be excessive unless the voltage between theelectrodes of the master oscillator MO and the power oscillator PO issuppressed. Accordingly, in this case, the gas in the laser chamber 10of the master oscillator MO may be partially exhausted (S608 mo).

Meanwhile, in the case where relationships where V<VL<VH andEmo<Emomin<Emomax are present (S596: YES), it can be understood that theamplification rate of the power oscillator PO is excessive and theoutput of the power oscillator PO will be excessive unless the voltagebetween the electrodes of the master oscillator MO and the poweroscillator PO is suppressed. Accordingly, in this case, the gas in thelaser chamber 20 of the power oscillator PO may be partially exhausted(S608 po).

In the case where the voltage V fulfils the relationship of VL<V<VH(S591: NO and S594: NO), the gas pressure control need not be carriedout.

Note that in the case where relationships where VL<VH<V andEmomin<Emo<Emomax are present (S593: NO), the gas pressure control neednot be carried out, and the second laser gas may be injected into thelaser chambers of the master oscillator MO and the power oscillator PO,respectively.

Meanwhile, in the case where relationships where V<VL<VH andEmomin<Emo<Emomax are present (S596: NO), the gas pressure control neednot be carried out, and the gases in the laser chambers of the masteroscillator MO and the power oscillator PO, respectively, may bepartially exhausted.

The control aside from that described above may be the same as thatdescribed in the fourth embodiment.

9. Sixth Embodiment MOPO System Including Ring Resonator

FIG. 30A schematically illustrates the configuration of an excimer lasersystem according to a sixth embodiment. FIG. 30B schematicallyillustrates the configuration of the power oscillator PO indicated inFIG. 30A. The sixth embodiment differs from the third embodiment in thatthe power oscillator PO can be configured using a ring resonator, asopposed to the third embodiment, in which the power oscillator PO isconfigured using a Fabry-Perot resonator.

The excimer laser system according to the sixth embodiment may include,in addition to the excimer laser apparatus according to the firstembodiment: high-reflecting mirrors 18 a through 18 c; the laser chamber20; the pair of electrodes 21 a and 21 b; a partially-reflecting mirror(output coupling mirror) 24; and high-reflecting mirrors 25 a through 25c. Furthermore, a charger, a pulse power module (PPM), a pressuresensor, an optical sensor module, and so on, which are not illustrated,may also be included.

The laser light outputted from the master oscillator MO may beintroduced into the partially-reflecting mirror (output coupling mirror)24 of the power oscillator PO via the high-reflecting mirrors 18 athrough 18 c.

The power oscillator PO may amplify the laser light by the laser lightpassing within the laser chamber 20 multiple times along a ring-shapedoptical path configured by the high-reflecting mirrors 25 a through 25 cand the partially-reflecting mirror 24.

The laser light amplified by the power oscillator PO can then beoutputted as output laser light via the partially-reflecting mirror(output coupling mirror) 24.

The configuration may be the same as that described in the thirdembodiment in other respects.

The aforementioned descriptions are intended to be taken only asexamples, and are not to be seen as limiting in any way. Accordingly, itwill be clear to those skilled in the art that variations on theembodiments of the present disclosure can be made without departing fromthe scope of the appended claims.

The terms used in the present specification and in the entirety of thescope of the appended claims are to be interpreted as not beinglimiting. For example, wording such as “includes” or “is included”should be interpreted as not being limited to the item that is describedas being included. Furthermore, “has” should be interpreted as not beinglimited to the item that is described as being had. Furthermore, themodifier “a” or “an” as used in the present specification and the scopeof the appended claims should be interpreted as meaning “at least one”or “one or more”.

1-10. (canceled)
 11. An excimer laser system comprising: a first excimerlaser apparatus that includes a first laser chamber containing a gas, atleast a pair of first electrodes disposed within said first laserchamber, and a first resonator disposed sandwiching said first laserchamber; a second excimer laser apparatus that includes a second laserchamber containing a gas, at least a pair of second electrodes disposedwithin said second laser chamber, and a second resonator disposedsandwiching said second laser chamber, and that amplifies laser lightoutputted from said first excimer laser apparatus; at least one powersource unit that supplies a voltage between said first electrodes andsaid second electrodes; a gas supply unit, connected to a firstreceptacle that holds a first laser gas containing halogen gas and asecond receptacle that holds a second laser gas having a lower halogengas concentration than said first laser gas, that supplies said firstlaser gas and said second laser gas to the interiors of said first laserchamber and said second laser chamber; a gas exhaust unit that partiallyexhausts gas from within said first laser chamber and said second laserchamber; and a gas control unit that controls said gas supply unit andsaid gas exhaust unit, wherein said gas control unit selectivelyperforms: a first gas pressure control in which said gas supply unitsupplies said second laser gas to the interior of said first laserchamber or said gas exhaust unit partially exhausts gas from within saidfirst laser chamber; a second gas pressure control in which said gassupply unit supplies said second laser gas to the interior of saidsecond laser chamber or said gas exhaust unit partially exhausts gasfrom within said second laser chamber; a first partial gas replacementcontrol in which said gas supply unit supplies said first laser gas andsaid second laser gas to the interior of said first laser chamber andsaid gas exhaust unit partially exhausts gas from within said firstlaser chamber sequentially; and a second partial gas replacement controlin which said gas supply unit supplies said first laser gas and saidsecond laser gas to the interior of said second laser chamber and saidgas exhaust unit partially exhausts gas from within said second laserchamber sequentially.
 12. The excimer laser system according to claim11, wherein said gas control unit selectively performs: said first gaspressure control; said second gas pressure control; said first partialgas replacement control; said second partial gas replacement control; afirst halogen gas filling control in which said gas supply unit suppliessaid first laser gas to the interior of said first laser chamber andsaid gas exhaust unit partially exhausts gas from within said firstlaser chamber sequentially; and a second halogen gas filling control inwhich said gas supply unit supplies said first laser gas to the interiorof said second laser chamber and said gas exhaust unit partiallyexhausts gas from within said second laser chamber sequentially.
 13. Theexcimer laser system according to claim 11, wherein said power sourceunit includes a single power storage unit that stores electrical energy,and said single power storage unit supplies a voltage both between saidfirst electrodes and between said second electrodes.
 14. An excimerlaser apparatus comprising: a laser chamber containing a gas; at least apair of electrodes disposed within said laser chamber; a power sourceunit that supplies a voltage between said electrodes; a gas supply unit,connected to a first receptacle that holds a first laser gas containinghalogen gas and a second receptacle that holds a second laser gas havinga lower halogen gas concentration than said first laser gas, thatsupplies said first laser gas and said second laser gas to the interiorof said laser chamber; a gas exhaust unit that partially exhausts gasfrom within said laser chamber; and a gas control unit that controlssaid gas supply unit and said gas exhaust unit, wherein said gas controlunit selectively performs: partial gas replacement control in which saidgas supply unit supplies said first laser gas and said second laser gasto the interior of said laser chamber and said gas exhaust unitpartially exhausts gas from within said laser chamber sequentially; andhalogen gas filling control in which said gas supply unit supplies saidfirst laser gas to the interior of said laser chamber and said gasexhaust unit partially exhausts gas from within said laser chambersequentially.
 15. The excimer laser apparatus according to claim 14,wherein said gas control unit: measures a repetition rate of laser lightoutputted from said laser chamber; and calculates a correction time byperforming a correction computation on a predetermined amount of timebased on said repetition rate; and performs the next partial gasreplacement control when said correction time has elapsed following theperformance of the previous partial gas replacement control.
 16. Anexcimer laser system comprising: a master oscillator, including a firstlaser chamber containing a gas and a first pressure detection unit thatdetects a pressure within said first laser chamber, that outputs laserlight; a power oscillator, including a second laser chamber containing agas and a second pressure detection unit that detects a pressure withinsaid second laser chamber, that amplifies and outputs the laser lightoutputted by said master oscillator; a gas supply unit, connected to afirst receptacle that holds a first laser gas containing halogen gas anda second receptacle that holds a second laser gas having a lower halogengas concentration than said first laser gas, that includes a pluralityof valves for selectively supplying or stopping the supply of said firstlaser gas and said second laser gas to the interiors of said first laserchamber and said second laser chamber; a gas exhaust unit that exhaustsgas from within said first laser chamber and said second laser chamber;and a gas control unit, connected to said first and second pressuredetection units, that controls said gas supply unit and said gas exhaustunit, wherein said gas control unit calculates and holds halogen gaspartial pressure values for the respective first and second laserchambers based on pressures and exhaust amounts from before and afterthe supply of the first and second laser gases, and calculates a firstpredetermined pressure, a second predetermined pressure, a thirdpredetermined pressure, and a fourth predetermined pressure based on thelatest halogen gas partial pressure value; and said gas control unitselectively performs: a first gas replacement control in which saidfirst laser gas is supplied to the interior of said first laser chamberup to the first predetermined pressure, said second laser gas issupplied up to the second predetermined pressure, and the gas withinsaid first laser chamber is exhausted to the pressure present before thesupply of said first laser gas; and a second gas replacement control inwhich said first laser gas is supplied to the interior of said secondlaser chamber up to the third predetermined pressure, said second lasergas is supplied up to the fourth predetermined pressure, and the gaswithin said second laser chamber is exhausted to the pressure presentbefore the supply of said first laser gas.